Nonsolvent-Induced Phase Separation-Jet Spinning: An Innovative Technique for Producing Cellulosic Nanofilms, Suspensions, and Nanofilm-Based Sponges

Abstract

The development of biobased porous materials using straightforward procedures remains challenging. This study introduces nonsolvent-induced phase separation-jet spinning (NIPS-JS), an innovative technique for fabricating cellulose acetate nanofilms. Coupling nonsolvent-induced phase separation (NIPS) with the turbulent mixing effects of high-velocity coaxial jets, NIPS-JS, achieves rapid and efficient nanofilm formation (40-50 nm thickness), demonstrating production rates exceeding 0.8 g·min^-1 and possessing adjustable parameters for optimization. The NIPS-JS technique holds promise for processing of diverse polymeric materials undergoing NIPS. Furthermore, this study demonstrates a novel application of NIPS-JS films for fabricating ultralight cellulosic sponges using cryo-templating and lyophilization, reducing the use of organic solvents and chemical cross-linkers. The resulting monolithic, three-dimensional networks, stabilized by robust lamination of individual thin films, exhibit ultralow density (5-10 kg·m^-3), high porosity (>99%), and excellent stability. Notably, the addition of 0.2-1 wt % ethanol enhances the reproducibility of the cryo-templating step and minimizes shrinkage. This cost-effective and scalable approach offers a promising pathway for the production of innovative porous materials without chemical cross-linkers.

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Schematic illustration of the cellulose acetate nanofilm and sponge preparation process. The process involves three steps: (a, b) nanofilm fabrication by the NIPS-JS technique, (c) polymer suspension preparation, and (d) sponge preparation via cryo-templating and lyophilizing techniques.

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(a) Microscope image, (b) SEM image, and (c) TEM image of the NIPS-JS as-spun polymer film. (d) Size distribution of the polymer suspension. (e) Illustration of the mechanism of the NIPS-JS technique. (f) Illustration of a ternary phase diagram representing the phase transition during the spinning process.

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(a–c) SEM images of the sponge and (d) cell wall surface. (e) X-ray CT reconstructed the sponge’s 3D structure and (f–h) projection images.

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Schematic illustration of the sponge-making process mechanism via the cryo-templating technique.

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Marginal distributions of sponge properties (height, diameter, shrinkage, and density) across levels of polymer suspension concentration (SUS; 0.24%, 0.3%, 0.4%) and ethanol concentration (EtOH; 0.2%, 0.5%, 1%). Plots a–d show the distribution of height, diameter, shrinkage, and density at different SUS levels, aggregated across all EtOH levels. Plots e–h show the distribution of height, diameter, shrinkage, and density at different EtOH levels, aggregated across all SUS levels.

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SEM images of sponges fabricated at suspension concentrations of (a, d, g) 0.24%, (b, e, h) 0.3%, and (c, f, i) 0.4% and ethanol concentration of (a–c) 1%, (d–f) 0.5%, and (g–i) 0.2%. (j) Contour plot of the first-order response surface of the shrinkage-dependent variable drawn in the plane of EtOH and Sus variables; the blue rectangle represents the fitted region; the arrow represents the path of improvement toward optimum conditions.